A conventional pneumatic stapler is disclosed in FIG. 1, and generally includes a barrel with a nose portion 3 through which staples are ejected therefrom, a handle connected to the barrel, and a magazine 1 for storing the staples is connected to the nose portion 3. The handle includes a connection member 4 which is fixed to a fixed portion 10 of the magazine 1 and a movable plate 11 is slidably connected to the fixed portion 10 so that the staples are stored in a space between the movable plate 11 and the fixed portion 10. A locking device 2 is pivotably connected to a protrusion 13 on the fixed portion 10 by a pin 14 and includes a lever 20 and a hook portion 21. The pin 14 is located between the lever 20 and the hook portion 21 so that when pivoting the lever 20, the hook portion 21 is moved between a locked position as shown in FIG. 1 to hook on a bottom of the movable plate 11, and a unlock position as shown in FIG. 3 to allow the movable plate 11 slidably removed from the fixed portion 10. As shown in FIG. 2, when one of more than one staples 50 are deformed by the impact from the push plate 51, the deformed staples 50 applies a force to the rest of the staples 50 in the magazine 1 and the force might unhooks the hook portion 21 as shown in FIG. 2. Therefore, the movable plate 11 is loosened and the staples 50 cannot be properly fed to the nose portion 3. Besides, when loading the staples 50, the user has to hold the handle by one hand and the other hand operates the lock device 3. This requires both hands to complete the loading action and is not convenient for the users during working.
The present invention intends to provide a locking device that is operated by only the hand holding the handle and effectively prevents the movable plate from loosing when the staples are deformed.